I know what you mean bro. Why can’t we all speak American like normal people?
It's a natural process when people come over that it generally takes a generation or two before their native language becomes secondary or significantly less prominent. Asians, Greeks, Italians, Russians, etc. undergo a similar process.
Americans who immigrate to other foreign language countries, most commonly Mexico, European Union (all European countries), Costa Rica, United Arab Emirates, China (yes China) etc., etc., have a tendency
to establish themselves in or near American communities as well, particularly in non-English speaking foreign countries. Obviously moving to England isn't a big transition or Canada unless you move to Quebec.
I had a brother, a mining engineer who emigrated to Peru in the 90's. We weren't that close, I didn't talk to him for over a dozen years and one day out of the blue he called me and I didn't know who he was. He sounded Peruvian, accent and all. For many years I was a well-heeled traveller. Even though areas of the world are unique we fundamentally are remarkably the same in how we slowly but surely cope with change, long term living elsewhere.